Molded case circuit breakers and earth leakage circuit breakers are known as protective devices in a low voltage distribution system. An earth leakage circuit breaker now manufactured in Japan generally has a construction with components for over current protection function and components for ground-fault protection function in a monolithic main housing. In order to improve the ease of use in the user side, an earth leakage circuit breaker has a common external dimension of the main housing shared by a molded case circuit breaker that has the same ampere frame (AF), and installs the functional components mentioned above in the main housing.
FIG. 5 shows a circuit diagram of an earth leakage circuit breaker, and FIGS. 6 and 7 show a construction of a circuit breaker of prior art. In FIG. 5, the reference numeral 1 designates a three-phase main circuit; the reference numeral 2, an open-close contact of the main circuit 1; the reference numeral 3, a zero-phase current transformer for detecting an earth leakage current with a primary winding of the main circuit 1; the reference numeral 4, an earth leakage detection circuit (an IC) for detecting occurrence of an earth leakage event on the basis of a secondary output from the zero-phase current transformer 3; the reference numeral 5, a power supply circuit for the earth leakage detection circuit 4; the reference numeral 6, a trip coil to open the open-close contact 2 on the basis of an output signal from the earth leakage detection circuit 4 (a plunger type electromagnet combined with an operation slider linking to an open-close mechanism of the circuit breaker); the reference numeral 7, a sensitivity current-switch for variably set a sensitivity current of the earth leakage circuit breaker (a slide switch); the reference numeral 8, an action time switch for variably set an action time (a slide switch); and the reference numeral 9, an earth leakage test switch (a push button switch).
In the construction of the earth leakage circuit breaker shown in FIG. 6, the reference numeral 10 designates a main housing (a lower case) of the earth leakage circuit breaker; the reference numeral 11, terminals at the supply side; the reference numeral 12, terminals at the load side; the reference numeral 13, an open-close operation handle; the reference numeral 14, an open-close mechanism; the reference numeral 15, an arc extinguishing chamber for the main circuit contact 2 (FIG. 5); and the reference numeral 16, an earth leakage trip unit. Here, the zero-phase current transformer 3 shown in FIG. 5 is disposed behind the load side terminals 12. A circuit board (a printed circuit board) mounting an IC of the earth leakage detection circuit 4 is accommodated in a case and disposed beside the zero-phase current transformer 3 in the main housing 10.
The earth leakage trip unit 16, on the other hand, is disposed beside the open-close operation handle 13 and accommodated in the central region of the main housing 10. The earth leakage trip unit 16 is provided with, as shown in FIG. 7, a trip coil 6 and an earth leakage indicating button 17 that acts in response to the trip coil action in the lower portion of a unit case 16a, and a sensitivity current-switch 7, an action time switch 8, an earth leakage test switch 9 and a connector 18 in the upper portion of the unit case. In the condition with a cover (not shown) put on the main housing 10, grips of the switches 7, 8, 9, and the earth leakage indicating button 17 are exposing outside the cover through openings formed in the cover.
Lead wires 19 running in the main housing 10 performs electrical connections between the circuit board of the earth leakage detection circuit 4 disposed beside the zero-phase current transformer 3 and the components including the trip coil 6 and the switches 7, 8 of the earth leakage trip unit 16 disposed beside the open-close operation handle 13. (See Patent Document 1: Japanese Utility Model Publication No. H3-118536).
The earth leakage circuit breaker having the conventional structure described above involves the following problems. As shown in FIG. 6, the zero-phase current transformer 3 and the earth leakage trip unit 16 are disposed at separate places in the main housing, and the circuit board of the earth leakage detection circuit 4 that is disposed beside the zero-phase current transformer 3 and the components of the earth leakage trip unit 16 including the trip coil 6, a sensitivity current-switch 7, and action time switch 8, and the earth leakage test switch 9 are connected by a connector 18 and lead wires 19. Moreover, the lead wires 19 thread their way through other components installed in the main housing 10. As a result, the lead wires are vulnerable to adverse affections of external noises, and arc gas and heat generated in the current interruption. Therefore, it is necessary for the lead wires to be protected against the external noises, and the arc gas and heat. In addition, the wiring work of the lead wires 19 takes a lot of time and may cause troubles, and thus, raises the production costs.
It is therefore an object of the present invention to solve the problems stated above and provide an earth leakage circuit breaker with an improved construction of an earth leakage trip unit, thereby reducing the number of components for earth leakage protection function and achieving space-saving and cost reduction of the circuit breaker.
Further objects and advantages of the invention will be apparent from the following description of the invention.